Carbon foam thermal core

ABSTRACT

A cold storage panel, which includes a carbon foam core having a high ratio of compressive strength to density, desirable fire retardant properties, and resistance to environmental stress. The carbon foam insulated panel also includes a first layer and a second layer bound to a first surface and second surface of the carbon foam core. Applications of the carbon foam structural insulated panel include structural and fire retardant elements of residential and commercial refrigerators and freezers, food lockers, coolers, and the like.

RELATED APPLICATION

This application is a continuation-in-part of copending and commonlyassigned U.S. Patent Application having Ser. No. 11/314,975, entitled“Carbon Foam Structural Insulated Panel” filed on Dec. 21, 2005 in thenames of Miller, Griffin and Segger, the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to the use of a carbon foam material asthe core for structural panels for cold storage applications, such ascommercial and residential refrigerators and freezers, food lockers,coolers, refrigerated rooms and holds, and the like. More particularly,the present invention relates to the use of carbon foam in insulatedpanels which provide insulation while also being non-flammable and whichdo not release noxious gases when exposed to flame.

2. Background Art

Many cold storage panels are formed using a core material of an expandedpolymeric foam like expanded polystyrene (EPS). The EPS or other foam isconventionally sandwiched between outer panels depending on the specificapplication. For instance, when the panel is used to form a relativelylarge structure such as a food locker or refrigerated room, the foam canbe sandwiched between layers of oriented strand board, fiber board,plywood, or other like materials. Alternatively, the outer layers can beformed of a metal sheet, such as a thin layer of steel. When the panelis used to form a smaller structure, such as a cooler or a refrigeratoror freezer, the core is sandwiched between a plastic material such as ahigh density polyethylene (HDPE). While this type of panel is wellunderstood and possesses adequate insulative value, EPS and otherpolymeric materials are flammable when exposed to heat, are subject tochemical degradation and emit noxious gases when burned.

What is desired, therefore, is a core material for a panel for coldstorage applications which possesses at least adequate insulative value(preferably a thermal R value of at least about 2, and as high as about4 or higher), while being relatively non-flammable, resistant tochemical degradation and which does not emit noxious gases when exposedto flame. The desired core material should also be light weight, have ahigh strength to density ratio, can be recycled, can be used in thinnersections, is inert and non-corrosive and resists deterioration overtime. Certain carbon foams provide just such a material.

In Hardcastle et al. (U.S. Pat. No. 4,425,396) an insulating panel isdisclosed with a synthetic organic polymeric foam with protectiveweathering layers comprised of multiple thermoplastic sheets.

Cahill (U.S. Pat. No. 6,656,858) describes a lightweight laminate wallcomprised of a low density layer of from about 0.5 to 3 pounds per cubicfoot and a second, reinforcing layer of a polymeric fabric. Thesestructures are lightweight, have a low moisture resistance and meetbuilding code requirements regarding transverse wind loading.

Porter (U.S. Pat. No. 6,599,621) describes a structural insulated panel(SIP) with high strength and resistance to fire and particularly towater and changes in humidity. The disclosed structures are comprised ofan inner insulating core with a gypsum fiberboard on one face of theinsulating core and an oriented strand board on the second face of theinsulating core. Preferably, the insulating core is comprised of aplastic foam such as expanded polystyrene or urethane which is bonded toboth the gypsum fiberboard and the oriented strand board.

Porter (U.S. Pat. No. 6,588,172) describes the incorporation of alaminated layer of plastic impregnated paper into a SIP to increase thepanel's tensile strength while rendering it impervious to moisture. Thislayer is typically situated between the gypsum board and plastic foamcore, adhered through a conventional bonding agent.

Parker (U.S. Pat. No. 4,628,650) describes a SIP with a foam core with alayer having an overhang projecting from the foam core edges. Theoverhang is situated to facilitate an effective seal between adjacentSIPs, providing better thermal insulation. Additionally, the core of thepanels has channels through the structure for the placement of joists,studs or rafters.

Clear (U.S. Pat. No. 6,079,175) describes a SIP of cementitious materialfor building structures. A lightweight fill material such as bottom ash,cement and water is poured between spaces of two outermost ribs, whichis claimed to provide insulation, strength and also rigidity to thepanel and therefore the structure the panel comprises. This SIP has theadvantage of being constructed in remote or more barren areas as it isfairly inexpensive to create.

Pease (U.S. Pat. No. 6,725,616) prepares an insulated concrete walleither cast or built with blocks which is attached to reinforcedinsulated strips. The patentee indicates that users will require lesstime and labor in making insulated using the patentee's method of fixingreinforced rigid foam to the surface of a concrete wall.

Pease (U.S. Pat. No. 6,892,507) describes a method and apparatus formaking an SIP with a rigid foam sheet. The rigid foam sheets havemultiple grooves in which reinforcing strips are situated. The stripsand rigid foam are then covered and bonded with a reinforcing sheet, thesheet providing both structural support and moisture retention.

SUMMARY OF THE INVENTION

The present invention provides a cold storage panel having a carbon foamcore, which is uniquely capable of being used in applications requiringgood insulative value, is non-flammable and resistant to chemicaldegradation and which does not emit noxious gases when exposed to flame.Moreover, since the carbon foam core material can provide adequateinsulative value in thinner sheets than conventional foams, theinventive panels can be made thinner than conventional panels, thusproviding significant space and cost savings.

The inventive carbon foam panel exhibits a density, compressive strengthand compressive strength to density ratio to provide a combination ofstrength and relatively light weight characteristics not heretoforeseen. In addition, the carbon lattice work of the carbon foam resistsboth charring and combustion while maintaining structural integrity inenvironmental conditions from high humidity to severely lowtemperatures. Furthermore, the carbon foam can be produced in a desiredsize and configuration and can be readily machined for a specific sizefor a cold storage panel.

More particularly, the inventive carbon foam cold storage panel has acarbon foam core with a density of from about 0.08 to about 0.16 gramsper cubic centimeter (g/cc) and a compressive strength of at least about5 megaPascals (MPa), more preferably at least about 6 MPa (measured by,for instance, ASTM C695). An important characteristic for the carbonfoam core when intended for use in larger scale applications such aswalk-in refrigerators and freezers, food lockers, etc. is a strength todensity ratio of at least about 20 MPa/g/cc, more preferably at leastabout 33 MPa/g/cc, most preferably at least about 37.5 MPa/g/cc, andhigher.

The inventive carbon foam panel should have the carbon foam core of arelatively uniform density both longitudinally and latitudinally forconsistent thermal insulation and strength characteristics throughoutthe panel. Specifically, the carbon foam should have a relativelyuniform distribution of pores in order to provide the required highcompressive strength, the pores being relatively isotropic. In addition,the carbon foam core should have a total porosity of about 65% to about95%, more preferably about 70% to about 95% to create the optimalstrength to density ratio of the carbon foam structural insulated panel.

Advantageously, to produce the carbon foam core, a polymeric foam block,particularly a phenolic foam block, is carbonized in an inert orair-excluded atmosphere, at temperatures which can range from about 500°C., more preferably at least about 800° C., up to about 3200° C. toprepare the carbon foams for use in the structural carbon foam panels.

Prior to the addition of outerlayers, the carbon foam core can betreated with a variety of coatings to improve the overall performance ofthe carbon foam cold storage panel. For example, an anti-oxidationcoating can be applied to the carbon foam to increase the longevity ofthe panel in highly oxidative conditions. Additionally, a fire retardantcoating could also be applied to the carbon foam core to furtherincrease the integrity of the carbon foam core and thus the panel, whenexposed to extreme temperatures.

Most commonly, the carbon foam core's first and second outerfaces areeach covered with a layer to form the inventive cold storage panel.Optionally, the outer layers may be comprised of oriented strand board(OSB) or a variety of gypsum board, or combinations thereof. Otherouterlayers exist including, but not limited to, a variety ofthermoplastics, metals, organic sheets, fiber impregnations, andcomposite boards.

The carbon foam core should be bound to the outer layers to constructthe cold storage panel. Binding may be through the use of materials suchas adhesives or cements which create a chemical interaction between theouter layers and the carbon foam core. These include binders specific tocarbon foam applications as well as general cements, mastics or hightemperature glue. Optionally, mechanical materials can be used.

Alternatively, the carbon foam can be formed having a higher density,about 0.2 to about 0.6 or higher, for instance, sealed, and used as acold storage panel without outerlayers.

An object of the invention, therefore, is a carbon foam panel havingcharacteristics which enable it to be used in cold storage applicationsrequiring an R value of at least about 2, and is non-flammable andresistant to chemical degradation and which does not emit noxious gaseswhen exposed to flame.

Another object of the invention is a cold storage panel having a carbonfoam core, with the structure of the carbon foam core having asufficiently high compressive strength to be used for high stressapplications.

Still another object of the invention is carbon foam panel where thecarbon foam core provides a fire retardant barrier, and which isextremely resistant to both combustion and charring.

Yet another object of the invention is an insulated foam panel which canbe produced in a desired size and configuration, where the carbon foamcore can be machined or joined with other similar carbon foam sheets toprovide larger carbon foam panels.

Another object of the invention is to provide an insulated panel whichis resistant to environmental stresses including high humidity andsevere temperature fluctuations.

Still another object of the invention is to provide a carbon foaminsulated panel where the carbon foam core provides adequate thermalinsulation to maintain a temperature differential between the one sideof the panel and the opposing side of the panel.

These aspects and others that will become apparent to the artisan uponreview of the following description can be accomplished by providing acarbon foam panel with a carbon foam core having an R value of at leastabout 2, more preferably as high as about 4 or higher. The foam corepreferably has a ratio of compressive strength to density of at leastabout 20 MPa/g/cc, especially a ratio of compressive strength to densityof at least about 33 MPa/g/cc, and most advantageously a ratio of atleast about 37.5 MPa/g/cc. The inventive cold storage panel has a carbonfoam core with a density of from about 0.08 g/cc to about 0.16 g/cc,more preferably of from about 0.11 g/cc to about 0.15 g/cc, and acompressive strength of at least about 5 MPa, more preferably at leastabout 6 MPa, with a porosity of between about 65% and about 95%.Furthermore the thermal conductivity of the carbon foam core is fromabout 0.06 W/mK to about 0.3 W/mK.

Furthermore, the carbon foam core can be produced by carbonizing apolymer foam article, especially a phenolic foam, in an inert orair-excluded atmosphere. The phenolic foam precursor for the carbon foamcore should preferably have a compressive strength of at least about 100pounds per square in (psi).

It is to be understood that both the foregoing general description andthe following detailed description provide embodiments of the inventionand are intended to provide an overview or framework of understanding tonature and character of the invention as it is claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a carbon foam cold storage panel in accordance withan embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Carbon foams in accordance with the carbon foam core of the presentinvention are prepared from polymeric foams, such as polyurethane foamsor phenolic foams, with phenolic foams being preferred. Phenolic resinsare a large family of polymers and oligomers, composed of a wide varietyof structures based on the reaction products of phenols withformaldehyde. Phenolic resins are prepared by the reaction of phenol orsubstituted phenol with an aldehyde, especially formaldehyde, in thepresence of an acidic or basic catalyst. Phenolic resin foam is a curedsystem composed of open and closed cells. The resins are generallyaqueous resoles catalyzed by sodium hydroxide at a formaldehyde:phenolratio which can vary, but is preferably about 2:1. Free phenol andformaldehyde content should be low, although urea may be used as aformaldehyde scavenger.

The foam is prepared by adjusting the water content of the resin andadding a surfactant (eg, an ethoxylated nonionic), a blowing agent (eg,pentane, methylene chloride, or chlorofluorocarbon), and a catalyst (eg,toluenesulfonic acid or phenolsulfonic acid). The sulfonic acidcatalyzes the reaction, while the exotherm causes the blowing agent,emulsified in the resin, to evaporate and expand the foam. Thesurfactant controls the cell size as well as the ratio of open-to-closedcell units. Both batch and continuous processes are employed. In thecontinuous process, the machinery is similar to that used for continuouspolyurethane foam. The properties of the foam depend mainly on densityand the cell structure.

The preferred phenol is resorcinol, however, other phenols of the kindwhich are able to form condensation products with aldehydes can also beused. Such phenols include monohydric and polyhydric phenols,pyrocatechol, hydroquinone, alkyl substituted phenols, such as, forexample, cresols or xylenols; polynuclear monohydric or polyhydricphenols, such as, for example, naphthols, p.p′-dihydrexydiphenyldimethyl methane or hydroxyanthracenes.

The phenols used to make the foam starting material can also be used inadmixture with non-phenolic compounds which are able to react withaldehydes in the same way as phenol.

The preferred aldehyde for use in the solution is formaldehyde. Othersuitable aldehydes include those which will react with phenols in thesame manner. These include, for example, acetaldehyde and benzaldehyde.

In general, the phenols and aldehydes which can be used in the processof the invention are those described in U.S. Pat. Nos. 3,960,761 and5,047,225, the disclosures of which are incorporated herein byreference.

Optionally, the carbon foam core of the inventive panel can be createdfor an increased oxidation resistance by the specific inclusion ofcompounds solely for improving the oxidation resistance of the carbonfoam. Such solid oxidation inhibiting additives include ammoniumphosphate, aluminum phosphate, zinc phosphate or boric acid. Anadditional characteristic of the oxidation inhibiting additives is thatthe additives can be added during either the resin production stage orthe phenolic foam forming stage of carbon foam production. Using eithermethod, the final carbonization of the phenolic foam results inphosphorous or boron retained within the carbon foam structure thatreduces the rate of oxidation of the carbon foam. Specifically,phosphorous or boron retained in the final carbon foam product fromabout 0.01% to about 0.5% by weight reduces the rate of oxidation byover 50%.

Alternatively, the carbon foam product can be treated with anoxidation-inhibiting agent after the completion of the carbonizationprocess but prior to the integration in the panel. The preferred methodwould be to impregnate the carbon foam with aqueous solutions ofphosphorous-containing materials such as ammonium phosphate, phosphoricacid, aluminum phosphate, or zinc phosphate, followed by a heattreatment to about 500° C. to simultaneously remove the water and fixthe phosphorous to the carbon. Additionally, water-soluble boroncompounds such as boric acid can be introduced in the above manner tocreate an oxidation-resistant carbon foam product.

The polymeric foam used as the starting material in the production ofthe carbon foam core should have an initial density which mirrors thedesired final density for the carbon foam which is to be formed. Inother words, the polymeric foam should have a density of about 0.08 g/ccto about 0.16 g/cc. The cell structure of the polymeric foam should beclosed with a porosity of between about 65% and about 95% and arelatively high compressive strength, i.e., on the order of at leastabout 100 psi, and as high as about 300 psi or higher.

In order to convert the polymeric foam to carbon foam, the foam iscarbonized by heating to a temperature of from about 500° C., morepreferably at least about 800° C., up to about 3200° C., in an inert orair-excluded atmosphere, such as in the presence of nitrogen. Theheating rate should be controlled such that the polymer foam is broughtto the desired temperature over a period of several days, since thepolymeric foam can shrink by as much as about 50% or more duringcarbonization. Care should be taken to ensure uniform heating of thepolymer foam piece for effective carbonization.

By use of a polymeric foam heated in an inert or air-excludedenvironment, a non-graphitizing glassy carbon foam is obtained, whichhas the approximate density of the starting polymer foam, but acompressive strength of at least about 5 MPa and, significantly, a ratioof strength to density of at least about 20 MPa/g/cc, more preferably atleast about 33 MPa/g/cc. The carbon foam has a relatively uniformdistribution of isotropic pores having, on average, an aspect ratio ofbetween about 1.0 and about 1.5.

Referring now to FIG. 1, there is revealed a partial side view of a coldstorage panel 10 with a carbon foam core 12 in accordance with one ofthe embodiments of the present invention.

Carbon foam core 12 and panel 10 are generally planar, though can beconstructed to meet a variety of specifications. Optionally, carbon foamcore 12 can be curved or possess rounded edges through either machiningor molding to best fit the desired cold storage application.

Cold storage panel 10 includes both the first outer layer 14 and secondouter layer 16 situated on the opposite outer surfaces of carbon foamcore 12. As with carbon foam core 12 and panel 10, both the first outerlayer 14 and the second outer layer 16 can possess a variety of shapesfor the desired application. The first outer layer 14 and the secondouter layer 16 can comprise similar or completely different materialsdepending upon the specific structural application of the panel. Thesematerials include typical construction materials such as plywood,oriented strand board, drywall, gypsum, cement composites, woodcomposites, or a variety of other rigid organic or inorganicconstruction boards. Furthermore, first outer layer 14 and second outerlayer 16 can also be impregnations of the above materials or includethermoplastics, resins, carbon composites, ceramic composites or avariety of other artificially created materials. In certain cases theselayers can include thin metal skins around carbon foam core 12, or outerlayer 14 and outer layer 16 can include hardened metal composites.Obviously, the selection of first outer layer 14 and the second outerlayer 16 will be based on the necessary tensile strength and fireretardant and insulative properties of the specific panel 10.Furthermore, first outer layer 14 and second outer layer 16 can be oftwo different materials where the use of panel 10 necessitates suchproperties. Other materials which can comprise either one or both of theouter layers 14 and 16 include but are not limited to the following:paper, reinforced paper composites, oriented strand board, fiberboard,drywall, gypsum, gypsum composites, wood, wood composites, plywood,thermoplastics, plastic composites, resins, metals, metal alloys, metalcomposites, and combinations thereof

In an additional embodiment, sheets of compressed particles ofexfoliated graphite are incorporated into the panel, situated in contactwith the carbon foam core. These graphite sheets can either be on oneside or both sides of the carbon foam core, in between the outer layersand the carbon foam core. Suitable sheets of compressed particles ofexfoliated graphite (often referred to in the industry as “flexiblegraphite”) can be produced by intercalating graphite flakes with asolution containing, e.g., a mixture of nitric and sulfuric acids,expanding or exfoliating the flakes by exposure to heat, and thencompressing the exfoliated flakes to form coherent sheets. Theproduction of sheets of compressed particles of exfoliated graphite isdescribed in, for instance, U.S. Patent Application Publication No.US-2005-0079355-A1, the disclosure of which is incorporated herein byreference.

By the incorporation of sheets of compressed particles of exfoliatedgraphite with the carbon foam core, a superior fire retardant structureis created. The anisotropic thermal properties of an compressedexfoliated graphite sheet on one or both opposing sides of the carbonfoam core provide significant improvements in thermal management.

The first outer layer 14 and the second outer layer 16 are connected tothe carbon foam core 12 through a bonding or adhesive material 18. Thisbonding or adhesive material 18 can include chemical bonding agentssuitable for specific applications ranging from high temperatureconditions to exposure to an acidic environment. Different chemicalbonding materials include adhesives, glues, cement, and mastic.Optionally, the first outer layer 14 and second outer layer 16 can beattached to the carbon foam core 12 through mechanical materials. Whilethis method does affect the integrity and uniform characteristics ofcarbon foam core 12, mechanical connects are available for little costand are extremely quick to complete. Various mechanical attachingmethods of attaching both the first outer layer 14 and the second outerlayer 16 to the carbon foam core 12 include but are not limited tonails, studs, screws, braces, struts, fasteners, staples, andcombinations thereof. Additionally, the first outer layer 14 and thesecond outer layer 16 can be compressedly bound to the carbon foam corethrough a series of high compression treatments of the outer layers 14and 16 to the carbon foam core. While less permanent than either themechanical or chemical attachment options, this attach type introducesno extra chemical compounds or weakens the structural integrity ofcarbon foam core 12 as does either the chemical or mechanical attachmentmethods.

First coating 20 and second coating 22 are both optional and applied tocarbon foam core 12 to alter the carbon foam core's 12 properties.Specifically, first coating 20 and second coating 22 can be identical ordifferent, depending upon the conditions and necessary properties of thecarbon foam core 12. For example, first coating 20 and second coating 22can both be a coating to improve the fire retardant properties of thecarbon foam core 12. Additionally, the first coating 20 could be anoxidation resistant coating where as the second coating 22 could be afire retardant coating where one side of panel 10 would be more likelyexposed to an oxidation atmosphere while the other side of panel 10would have a greater likelihood of being exposed to fire. Also, firstcoating 20 and second coating 22 are optionally applied; for manyapplications of cold storage panel 10, neither first coating 20 norsecond coating 22 are necessary.

With carbon foam core 12 as the insulating layer in cold storage panel10, panel 10 has an inherent fire retardant/resistant property. As otherinsulating materials merely preclude oxygen from the structuralinsulating panel's structure, carbon foam core 12 is extremely resistantto both combustion or charring. Specifically, carbon foam core 12 ismainly linked carbons with relatively few other elements present withinits foam structure. As such, little exists for combustion, other thanthe simple oxidation of the carbon of carbon foam core 12. For thisoxidation to occur, temperatures have to reach rather extremetemperatures, making carbon foam core 12 very suitable for applicationswhere fire retardant structures are required.

Similarly, carbon foam core 12 is resistant to many environmentalstresses including insects, humidity, and heat. Carbon foam is anextremely hard substance, lending itself poorly to insect habitationwhile its chemical and structural properties are virtually not alteredby a change in humidity. Furthermore, first outer layer 14 and secondouter layer 16 can be selected for the specific environmentalapplications to which panel 10 will be subjected.

Finally, cold storage panel 10 and its fire retardant nature, superiorstrength to density ratio as well as resistance to chemical degradationmake panel 10 suitable for a wide variety of cold storage applications.These abovementioned applications are feasible uses of the inventivecarbon foam structural insulated panel yet by no mean include allapplications for which this invention is feasible.

Accordingly, by the practice of the present invention, cold storagepanels with carbon foam cores, having heretofore unrecognizedcharacteristics are prepared. These panels with carbon foam coresexhibit exceptionally high compressive strength to density ratios, muchimproved fire retardance and environmental stability, making themuniquely effective at cold storage applications, ranging fromrefrigerators and freezers, to food lockers and coolers.

The disclosures of all cited patents and publications referred to inthis application are incorporated herein by reference.

The above description is intended to enable the person skilled in theart to practice the invention. It is not intended to detail all of thepossible variations and modifications that will become apparent to theskilled worker upon reading the description. It is intended, however,that all such modifications and variations be included within the scopeof the invention that is defined by the following claims. The claims areintended to cover the indicated elements and steps in any arrangement orsequence that is effective to meet the objectives intended for theinvention, unless the context specifically indicates the contrary.

1. A cold storage panel comprising a carbon foam material with a densityof from about 0.08 g/cc to about 0.16 g/cc.
 2. The panel of claim 1further comprising: a first outer layer bound to a first surface of thecarbon foam material; and a second outer layer bound to a second surfaceof the carbon foam material.
 3. The panel of claim 1 wherein the carbonfoam material has a ratio of compressive strength to density of at leastabout 20 MPa/g/cc.
 4. The panel of claim 1 wherein the carbon foammaterial has a thermal conductivity of from about 0.06 W/mK to about 0.3W/mK.
 5. The panel of claim 1 wherein the carbon foam material includesa coating on the carbon foam's exterior surface.
 6. The panel of claim 6wherein the coating improves fire retardancy of the carbon foammaterial.
 7. The panel of claim 6 wherein the coating improves oxidationresistance of the carbon foam material.
 8. The panel of claim 1 furthercomprising a layer of compressed particles of exfoliated graphite on atleast one surface of the carbon foam material.
 9. The panel of claim 2wherein the outer layers are selected from the group consisting ofpaper, reinforced paper composites, oriented strand board, fiberboard,drywall, gypsum, gypsum composites, wood, wood composites, plywood,thermoplastics, plastic composites, resins, metals, metal alloys, metalcomposites, and combinations thereof.
 10. A cold storage panelcomprising a carbon foam material having a ratio of compressive strengthto density of at least about 20 MPa/g/cc.
 11. The panel of claim 10further comprising: a first outer layer bound to a first surface of thecarbon foam material; and a second outer layer bound to a second surfaceof the carbon foam material.
 12. The panel of claim 10 wherein thecarbon foam material with a density of from about 0.08 g/cc to about0.16 g/cc.
 13. The panel of claim 10 wherein the carbon foam materialhas a thermal conductivity of from about 0.06 W/mK to about 0.3 W/mK.14. The panel of claim 10 wherein the carbon foam material includes acoating on the carbon foam's exterior surface.
 15. The panel of claim 14wherein the coating improves fire retardancy of the carbon foammaterial.
 16. The panel of claim 14 wherein the coating improvesoxidation resistance of the carbon foam material.
 17. The panel of claim10 further comprising a layer of compressed particles of exfoliatedgraphite on at least one surface of the carbon foam material.
 18. Thepanel of claim 11 wherein the outer layers are selected from the groupconsisting of paper, reinforced paper composites, oriented strand board,fiberboard, drywall, gypsum, gypsum composites, wood, wood composites,plywood, thermoplastics, plastic composites, resins, metals, metalalloys, metal composites, and combinations thereof